This is all helpful, thank you Tony and Mark.
Mark's snippet means changing the file name every time. What I am looking for is a way to set the filenames of each tiddler by entering it into its caption field upon creation of the tiddler. That way every time I update and export the tiddler I don't have to remember what filename I gave it. It just exports to that filename automatically. So I am looking at tweaking $:/core/ui/Buttons/export-tiddler from
baseFilename=<<currentTiddler>>
to something like
baseFilename=<<currentTiddler field="caption">>
but I don't know how to write it.
Dave